The invention relates generally to optical sensors and more particularly to refractive index waveguide sensors.
U.S. Pat. Nos. 4,929,049 and 5,026,139 and U.S. application Ser. No. 07/646,148, now U.S. Pat. No. 5,165,005, disclose optical sensors with thin film metal clads on an optical fiber or other waveguide structure which operate on the basis of refractive index. The clad is designed so that light leakage through the metal clad is a function of the refractive index of the surrounding medium, which varies with the presence of a target species. The metal clads may be made of adjacent segments of different metals. The metal clads can be selected with great specificity to a particular analyte. Presently these optical sensors are made of arbitrary length, typically one inch. It would be desirable to optimize the sensor length to increase sensitivity and to make the sensor as compact as possible for certain applications.
U.S. Pat. No. 4,913,519 describes an ice sensor which has a segmented clad with gaps formed on a fiber. The presence of air, water or ice in the gaps is determined from resulting changes in the transmission properties of the fiber caused by the change in refractive index.
U.S. Pat. No. 5,109,442 is directed to waterproofing a fiber optic sensor by applying hydrophobic polymers. A patterned polymer clad may be formed over the metal clad on a fiber.